onedspec
observatory = observatory
Observatory at which the spectra were obtained if not specified in the
image header by the keyword OBSERVAT. This parameter is used by several
tasks in the package through parameter redirection so this parameter may be
used to affect all these tasks at the same time. The observatory may be
one of the observatories in the observatory database, "observatory" to
select the observatory defined by the environment variable "observatory" or
the parameter observatory.observatory, or "obspars" to select the
current parameters set in the observatory task. See help for
observatory for additional information.
caldir =
Calibration directory containing standard star data. This parameter
is used by several tasks in the package through redirection. A list of
standard calibration directories may be obtained by listing the file
"onedstds$README"; for example:
cl> page onedstds$README
The user may copy or create their own calibration files and specify the directory. The directory "" refers to the current working directory.
interp = poly5 (nearest|linear|poly3|poly5|spline3|sinc)
Spectrum interpolation type used when spectra are resampled. The choices are:
nearest - nearest neighbor linear - linear poly3 - 3rd order polynomial poly5 - 5th order polynomial spline3 - cubic spline sinc - sinc function.le
version = ONEDSPEC V3: November 1991
Package version identification.
The onedspec package contains generic tasks for the reduction, analysis, and display of one dimensional spectra. The specifics of individual tasks may be found in their IRAF "help" pages. This document describes the general and common features of the tasks.
The functions provided in the onedspec package with applicable tasks are summarized in Table 1.
1. Graphical display of spectra
bplot - Batch plots of spectra
identify - Identify features and fit dispersion functions
specplot - Stack and plot multiple spectra
splot - Interactive spectral plot/analysis
2. Determining and applying dispersion calibrations
dispcor - Dispersion correct spectra
dopcor - Apply doppler corrections
identify - Identify features and fit dispersion functions
refspectra - Assign reference spectra to other spectra
reidentify - Automatically identify features in spectra
specshift - Shift spectral dispersion coordinate system
3. Determining and applying flux calibrations
calibrate - Apply extinction and flux calibrations to spectra
deredden - Apply interstellar extinction correction
dopcor - Apply doppler corrections
lcalib - List calibration file data
sensfunc - Create sensitivity function
standard - Tabulate standard star data
4. Fitting spectral features and continua
continuum - Fit the continuum in spectra
fitprofs - Fit gaussian profiles
sfit - Fit spectra and output fit, ratio, or difference
splot - Interactive spectral plot/analysis
5. Arithmetic and combining of spectra
sarith - Spectrum arithmetic
scombine - Combine spectra
splot - Interactive spectral plot/analysis
6. Miscellaneous functions
mkspec - Generate an artificial spectrum
names - Generate a list of image names from a string
sapertures - Set or change aperture header information
scopy - Select and copy spectra
sinterp - Interpolate a table of x,y to create a spectrum
slist - List spectrum header parameters
splot - Interactive spectral plot/analysis
There are other packages which provide additional functions or specialized tasks for spectra. Radial velocity measurements are available in the noao.rv package. The noao.imred package contains a number of packages for specific types of data or instruments. These packages are listed in Table 2.
argus - CTIO ARGUS reduction package
echelle - Generic Echelle spectral reductions
foe - Fiber Optic Echelle spectral reductions
goldcam - KPNO GOLDCAM reduction package
hydra - KPNO HYDRA (and NESSIE) reduction package
iids - KPNO IIDS spectral reductions
irs - KPNO IRS spectral reductions
kpcoude - KPNO Coude reduction package
specred - CTIO Spectrophotometric reduction package
Finally, there are non-NOAO packages which may contain generally useful software for spectra. Currently available packages are stsdas and xray.
See the separate help topic specwcs.
Changing the dispersion sampling of spectra, such as when converting to a constant sampling interval per pixel or a common sampling for combining or doing arithmetic on spectra, requires interpolation. The tasks which reinterpolate spectra, if needed, are dispcor, sarith, scombine, and splot.
The interpolation type is set by the package parameter interp. The available interpolation types are:
nearest - nearest neighbor linear - linear poly3 - 3rd order polynomial poly5 - 5th order polynomial spline3 - cubic spline sinc - sinc function
The default interpolation type is a 5th order polynomial.
The choice of interpolation type depends on the type of data, smooth verses strong, sharp, undersampled features, and the requirements of the user. The "nearest" and "linear" interpolation are somewhat crude and simple but they avoid "ringing" near sharp features. The polynomial interpolations are smoother but have noticible ringing near sharp features. They are, unlike the sinc function described below, localized.
In V2.10 a "sinc" interpolation option is available. This function has advantages and disadvantages. It is important to realize that there are disadvantages! Sinc interpolation approximates applying a phase shift to the fourier transform of the spectrum. Thus, repeated interpolations do not accumulate errors (or nearly so) and, in particular, a forward and reverse interpolation will recover the original spectrum much more closely than other interpolation types. However, for undersampled, strong features, such as cosmic rays or narrow emission or absorption lines, the ringing can be more severe than the polynomial interpolations. The ringing is especially a concern because it extends a long way from the feature causing the ringing; 30 pixels with the truncated algorithm used. Note that it is not the truncation of the interpolation function which is at fault!
Because of the problems seen with sinc interpolation it should be used with care. Specifically, if there are no undersampled, narrow features it is a good choice but when there are such features the contamination of the spectrum by ringing is much more severe than with other interpolation types.
In versions of the NOAO spectroscopy packages prior to V2.10 the dispersion units used were restricted to Angstroms. In V2.10 the first, experimental, step of generalizing to other units was taken by allowing the two principle spectral plotting tasks, splot and specplot, to plot in various units. Dispersion functions are still assumed to be in Angstroms but in the future the generalization will be completed to all the NOAO spectroscopy tasks.
The dispersion units capability of the plotting tasks allows specifying the units with the "units" task parameter and interactively changing the units with the ":units" command. In addition the 'v' key allows plotting in velocity units with the zero point velocity defined by the cursor position.
The units are specified by strings having a unit type from the list below along with the possible preceding modifiers, "inverse", to select the inverse of the unit and "log" to select logarithmic units. For example "log angstroms" to plot the logarithm of wavelength in Angstroms and "inv microns" to plot inverse microns. The various identifiers may be abbreviated as words but the syntax is not sophisticated enough to recognized standard scientific abbreviations such as mm for millimeter.
Table 1: Unit Types angstroms - Wavelength in Angstroms nanometers - Wavelength in nanometers millimicrons - Wavelength in millimicrons microns - Wavelength in microns millimeters - Wavelength in millimeters centimeter - Wavelength in centimeters meters - Wavelength in meters hertz - Frequency in hertz (cycles per second) kilohertz - Frequency in kilohertz megahertz - Frequency in megahertz gigahertz - Frequency in gigahertz m/s - Velocity in meters per second km/s - Velocity in kilometers per second ev - Energy in electron volts kev - Energy in kilo electron volts mev - Energy in mega electron volts z - Redshift
The velocity and redshift units require a trailing value and unit defining the velocity zero point. For example to plot velocity relative to a wavelength of 1 micron the unit string would be:
km/s 1 micron
Some additional examples of units strings are:
milliang megahertz inv mic log hertz m/s 3 inv mic z 5015 ang
SEE ALSO, apextract, longslit, rv, imred, specwcs,